IEA’s PIRLS (Progress in International Reading Literacy Study) provides trends in reading achievement at the fourth grade for 60-plus countries around the world. Assessed every 5 years since 2001 in a paper-and-pencil format, PIRLS in 2021 transitioned to a digital assessment in about half of the countries. These countries will participate in a unified digital assessment that integrates digitalPIRLS, a digital version of the PIRLS 2021 assessment presented through an innovative user interface, and ePIRLS, an assessment of online informational reading first administered in 14 countries on a voluntary basis in 2016. The remaining countries will administer PIRLS 2021 in paper-and-pencil format, as they did in previous assessment cycles. PIRLS 2021 will keep pace with the changing nature of fourth graders’ reading experiences, capture information (log data) about students’ reading strategies, and introduce operational efficiencies into the complex endeavor of an assessment conducted across thousands of schools internationally and in multiple languages. This chapter addresses the development of digitalPIRLS and ePIRLS undertaken by the TIMSS & PIRLS International Study Center at Boston College, including a discussion of the challenges associated with a transition to a digital assessment—including the development of items and a digital testing platform—and the opportunities a digital reading assessment presents.